Thin film transistor array panel for liquid crystal display having pixel electrode

ABSTRACT

A TFT array panel includes an insulating substrate, a gate line, a storage electrode line, a gate insulating layer, a semiconductor island formed on the gate insulating layer, and a data line and a drain electrode formed thereon. The data line and drain electrode are covered with a passivation layer. A pixel electrode is formed on the passivation layer and connected to the drain electrode through a contact hole. The TFT array panel is covered with an alignment layer rubbed approximately in a direction from the upper left corner to lower right corner of the TFT array panel or the pixel electrodes. The pixel electrode overlaps the gate line and data line and has an expansion located near the upper left corner of the pixel electrode to increase the width of the corresponding overlapping area between the pixel electrode and the gate line and/or data line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.12/570,505 filed on Sep. 30, 2009, which is a Continuation of U.S.patent application Ser. No. 11/873,767 filed Oct. 17, 2007 which is aContinuation of U.S. patent application Ser. No. 11/551,450, filed Oct.20, 2006, which is a Divisional of U.S. patent application Ser. No.10/317,591, filed Dec. 12, 2002, now U.S. Pat. No. 7,145,620, issuedDec. 5, 2006, which claims priority to Korean Application No.2002-31098, filed Jun. 3, 2002, the disclosures of which areincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a thin film transistor array panel fora liquid crystal display including a pixel electrode.

(b) Description of the Related Art

A liquid crystal display (“LCD”) is one of the most widely used flatpanel displays. An LCD includes two panels having field-generatingelectrodes and a liquid crystal layer interposed therebetween andcontrols the transmittance of light passing through the liquid crystallayer fly realigning liquid crystal molecules in the liquid crystallayer with voltages applied to the electrodes.

One of the most commonly used LCDs provides a plurality of planarfield-generating electrodes on one panel with switching elementsswitching the voltages applied to the electrodes and one large planarfield-generating electrode on the other panel, which is applied with afixed voltage or two swinging voltages. Thin film transistors (“TFTs”)are usually used as the switching elements, and the panel including theTFTs is called the “TFT array panel.”

The planar field-generating electrodes provided on respective panelsgenerate electric field perpendicular to the panels. Some of theelectric field lose that perpendicularity near the edges of theelectrodes.

A typical LCD further includes an alignment layer for determininginitial alignments of the liquid crystal molecules. One type of thealignment layer forces the director of the liquid crystal material to beparallel to the surface of the alignment layer (which is calledhomogeneous alignment), while another type forces the director to benormal to the surface (which is called hemeotropic alignment). A propersurface treatment of the alignment layer such as rubbing and lightexposure controls the tilt directions of the liquid crystal molecules.For example, the rubbing in a direction enforces the major axes of theliquid crystal molecules to tilt in that direction.

The combination of the irregularity of the electric field near the edgesof the field-generating electrodes and the compulsive alignment of theliquid crystal molecules using the surface treatment of the alignmentlayer may result in loss of control for the liquid crystal molecules.This effect is called disclination, which causes light leakage.

SUMMARY OF THE INVENTION

A thin film transistor array panel for a liquid crystal display isprovided, which includes: a substrate; a plurality of signal linesprovided on the substrate and including a gate line and a data lineinsulated from each other; a switching element electrically connected tothe gate line and the data line; a pixel electrode electricallyconnected to the switching element and overlapping at least one of thesignal lines via an insulator to form at least one overlapping area; anda rubbed aligment layer covering the pixel electrode, wherein at leastone portion of the at least one overlapping area near a startingposition of rubbing of the alignment layer is wider than other portionsof the at least one overlapping area.

According to an embodiment of the present invention, the pixel electrodehas an expansion forming the at least one portion of the at least oneoverlapping area.

According to another embodiment of the present invention, the pixelelectrode has a plurality of major edges, and at least one of the majoredges proceeds into the at least one of the gate line and the data linemore deeply than other major edges to form the at least one portion ofthe at least one overlapping area.

The switching element preferably includes a semiconductor layerelectrically connected to the gate line and the pixel electrode, and thesemiconductor layer extends along the data line. The switching elementfurther includes an ohmic contact interposed between the semiconductorlayer and the data line.

According to an embodiment of the present invention, the thin filmtransistor array panel further includes: a storage electrode separatedfrom the signal lines; id a storage conductor electrically connected tothe pixel electrode and overlapping the storage electrode via aninsulating layer. The storage conductor is directly connected to thethin film transistor.

It is preferable that the pixel electrode is located on the insulator,and the thin film transistor is located under the insulator.

Another thin film transistor array panel for a liquid crystal display isprovided, which includes: a substrate; a plurality of signal linesprovided on the substrate and including a gate line and a data line; agate insulating layer interposed between the gate line and the dataline; a switching element electrically connected to the gate line andthe data line; a pixel electrode electrically connected to the switchingelement; and a passivation layer interposed between the pixel electrodeand the data line and between the pixel electrode and the gate line,wherein the pixel electrode overlaps at least one of the signal lines toform at least one overlapping area and includes an expansion providinglarger width of a portion of the at least one overlapping area thanother portions of the at least one overlapping area.

The at least one of the signal lines preferably includes the gate line.

According to an embodiment of the present invention, the pixel electrodehas substantially a rectangular shape with four major edges includingfirst two major edges substantially parallel to the gate line and secondtwo major edges substantially parallel to the data line, and a portionof the first two major edges form the expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or the similar components, wherein:

FIG. 1 is a layout view of an exemplary TFT array panel for an LCDaccording to an embodiment of the present invention;

FIG. 2 is a sectional view of the TFT array panel shown in FIG. 1 takenalong the line II-II′;

FIG. 3 is a layout view of an exemplary TFT array panel for an LCDaccording to another embodiment of the present invention; and

FIGS. 4 and 5 are sectional views of the TFT array panel shown in FIG. 3taken along the lines IV-IV′ and V-V′, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown.

In the drawings, the thickness of layers and regions are exaggerated forclarity. Like numerals refer to like elements throughout. It will beunderstood that when an element such as a layer, region or substrate isreferred to as being “on” another element, it can be directly f-n theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly on” another element,there are no intervening elements, present.

FIG. 1 is a layout view of an exemplary TFT array panel according to anembodiment of the present invention, and FIG. 2 is a sectional view ofan exemplary LCD including the TFT array panel shown in FIG. 1 takenalong the line II-II′.

As shown in FIG. 2, an LCD according to an embodiment of the presentinvention includes a lower panel (“TFT array panel”) 100, an upper panel(“color filter panel”) 200 and a liquid crystal layer 3 interposedtherebetween.

The color filter panel 200 includes an insulating substrate 210, a blackmatrix 220, a plurality of color filters 230 and a reference electrode270 formed in sequence. In addition, an alignment layer 21 is providedon the reference electrode 270.

As shown in FIGS. 1 and 2, the TFT array panel 100 includes a pluralityof gate lines 121 and a plurality of storage electrode lines 131extending substantially in a transverse direction formed on aninsulating substrate 110. The gate lines 121 and the storage electrodelines 131 include either a single layer preferably made of material withlow resistivity such as silver, silver alloy, aluminum and aluminumalloy, or multiple layers including such a single layer and a layerpreferably made of material with good physical and electrical contactcharacteristics, such as Cr, Ti and Ta. A plurality of branches of eachgate line 121 form gate electrodes 124 of TFT's, and portions of storageelectrode lines 131 expand upward and downward to form storageelectrodes 133. A predetermined voltage such as a reference voltage or acommon electrode voltage (referred to as “a common voltage” hereinafter)is applied to the storage electrode lines 131 from an external source.The common voltage is also applied to the reference electrode 270 of thecolor filter panel 200.

The gate lines 121 and the storage electrode lines 131 are covered by agate insulating layer 140 preferably made of silicon nitride.

A plurality of semiconductor islands 154 preferably made of polysiliconor hydrogenated amorphous silicon are formed on the gate insulatinglayer 140 opposite the gate electrodes 124, and a plurality of pairs ofohmic contacts 163 and 165 preferably made of silicide or n+hydrogenatedamorphous silicon heavily doped with n type impurity are formed on thesemiconductor islands 154. One of each pair of ohmic contacts 163 and165 is separated from and disposed opposite to the other of the pairwith respect to a corresponding one of the gate electrodes 124.

A plurality of data lines 171 and a plurality of drain electrodes 175 ofthe TFTs are formed on the ohmic contacts 163 and 165 and the gateinsulating layer 140. The data lines 171 and the drain electrodes 175preferably include Cr, Mo, Mo alloy, Al, Al alloy, Ta and Ti, and mayhave a double-layered structure including a low-resistivity metal layerand a good-contact metal layer exhibiting good contact characteristicwith another material such as, IZO (indium zinc oxide). Examples of thedouble-layered structure are an Al (or Al alloy) layer End a Cr layer;and an Al (or Al alloy) layer and a Mo (or Mo alloy) layer.

The data lines 171 extend substantially in a longitudinal direction anintersect the gate lines 121, and a plurality of branches of each dataline 171 form source electrodes 173 of the TFTs. Each source electrodeextending to one 163 of the corresponding pair of the ohmic contacts 163and 165 is separated from and opposite the corresponding one of thedrain electrodes 175, which is located at least in part on the other 165of the pair of the ohmic contacts 163 and 165 with respect tocorresponding one of the gate electrodes 124. The drain electrodes 175extend onto the storage electrodes 133 to overlap.

The ohmic contacts 163 and 165 interposed between the semiconductorislands 154 and the data lines 171 and the drain electrodes 175 reducethe contact resistance therebetween.

A passivation layer 180 preferably made of silicon nitride, siliconoxide, low-permittivity insulating material such as SiO:C and SiO:Fobtained by chemical vapor deposition or low-permittivity organicinsulating material is formed on the data lines 171 and portions of thesemiconductor islands 154, which are not covered by the data lines 171and the drain electrodes 175.

The passivation layer 180 has a plurality of contact holes 182 and 183exposing end portions 179 of the data lines 171 and the drain electrodes175, and the passivation layer 180 and the gate insulating layer 140 hasa plurality of contact holes 181 exposing end portions 129 of the gatelines 121. Contact holes 181 and 182 are provided for electricalconnection between the signal lines 121 and 171 and respective drivingcircuits therefore.

A plurality of pixel electrodes 190 preferably made of transparentconductive material such as indium zinc oxide (“IZO”) and indium tinoxide (“ITO”) are formed on the passivation layer 180. Each pixelelectrode 190 is electrically connected to respective one of the drainelectrodes 175 through the corresponding contact hole 183.

Each pixel electrode 190 applied with voltages from the data lines 171generate electric fields in cooperation with a corresponding referenceelectrode provided on the other panel, and the variation of the appliedvoltage changes the orientations of liquid crystal molecules in a liquidcrystal layer between the two field-generating electrodes, the pixelelectrode 190 and the reference electrode. In view of electricalcircuits, each pair of the pixel electrode 190 and the referenceelectrode form a capacitor with liquid crystal dielectric far storingelectrical charges. The storage capacitance due to the overlap of thedrain electrodes 175 and the storage electrodes 133 enhances the chargestoring capacity of the liquid crystal capacitors.

Furthermore, a plurality of contact assistants 91 and 92 preferably madeof the same material as the pixel electrodes 190 are formed on thepassivation layer 180. The contact assistants 91 and 92 are connected tothe exposed end portions 129 and 179 of the gate and the data lines 121and 171 through the contact holes 181 and 182, respectively. One skilledin the art can readily appreciate that the contact assistants 91 and 92are not required but are preferred elements used to protect the exposedportions 129 and 179 of the gate and the data lines 121 and 171,respectively, and to complement the adhesiveness of the TFT array paneland the driving circuits.

An alignment layer 11 is formed on the TFT array panel 100. As indicatedby an arrow in FIG. 1, the alignment layer 21 is rubbed obliquely,preferably, about a direction from the upper left corner to the lowerright corner of the TFT array panel 100 or the pixel electrodes 190.

As shown in FIG. 1, the pixel electrodes 190 overlap the gate lines 121and the data lines 171 to increase aperture ratio, and it is preferablyadapted for low-permittivity passivation. The pixel electrode 190 issubstantially rectangular in shape with two major edges substantiallyparallel to the gate lines 121 and the other two edges substantiallyparallel to the data lines 171. The upper one of the two gate-paralleledges has an expansion 191 located near the upper left corner of thepixel electrode 190 to increase the width of the correspondingoverlapping area between the pixel electrode 190 and the gate line 121and/or the data line 171. In addition, the left one of the twodata-parallel edges of the pixel electrode proceeds into the data line171 more deeply than the right one to increase the width of the leftoverlapping area.

The orientation of the liquid crystal molecules in the liquid crystallayer 3 near the rubbing-starting corner of the pixel electrode 190 isdistorted since the tilt direction of the liquid crystal molecules dueto the rubbing makes a large angle with the field direction of thefringe field due to the discontinuity of the pixel electrode 190. Sincethe overlapping area between the pixel electrode 190 and the signallines 121 and 171 is light-blocked by the signal lines 121 and 171, theincreased overlapping area near the rubbing-starting corner means thatthe distorted area (or the disclination area) is sufficiently blocked bythe signal lines 121 and 171.

A TFT array panel for an LCD according to another embodiment of thepresent invention will be described in detail with reference to FIGS.3-5.

FIG. 3 is a layout view of an exemplary TFT array panel for an LCDaccording to another embodiment of the present invention, and FIGS. 4and 5 are sectional views of the TFT array panel shown in FIG. 3 takenalong the lines IV-VI′ and V-V′, respective y.

As shown in FIGS. 3-5, a TFT array panel of an LCD according to thisembodiment is almost the same as that of an LCD shown in FIGS. 1 and 2.

Different from the TFT array panel shown in FIGS. 1 and 2, a pluralityof pixel electrodes 190 have no expansion for increasing thecorresponding overlapping area. Instead, the upper one of twogate-parallel edges of the pixel electrode 190 proceeds in to the gateline 121 more deeply than the lower one to increase the width of theupper overlapping area.

Furthermore, a plurality of storage conductors 177 overlapping aplurality of storage electrode lines 131 are spaced apart from aplurality of drain electrodes 175. A plurality of contact holes 184 forexposing the storage conductors 177 are also provided to electricallyconnect the storage conductors 177 to the appropriate pixel electrodes190.

In addition, a plurality of gate electrodes 124 of TFTs are parts ofrespective gate lines 121 rather than their branches.

Furthermore, there are provided a plurality of semiconductor stripes andislands 151 and 157 under respective plurality of data lines 171, aplurality of drain electrodes 175 and the storage conductors 177. Eachsemiconductor stripe 151 extends onto the gate electrodes 124 along aplurality of source electrodes 173 and a plurality of drain electrodes175 to form channels of the TFTs. A plurality of ohmic contacts 161, 165and 167 are provided between the semiconductor stripes and islands 151and 157 and the data lines 171, the drain electrodes 175 and the storageconductors 177.

The semiconductor stripes 151 have similar planar shapes as the datalines 171 and the drain electrodes 175 except for channels of the TFTs.For example, although the data lines 171 are disconnected from the drainelectrodes 175 on the channels of the TFTs, the semiconductor stripes151 run continuously to form channels of the TFTs. The semiconductorislands 157 have similar planar shapes as the storage conductors 177.The ohmic contacts 161, 165 and 167 have similar planar shapes as thedata lines 171, the drain electrodes 175 and the storage conductors 177.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A method for manufacturing a thin film transistor array panelcomprising: forming a gate line on a substrate, the gate line comprisinga gate electrode; disposing a semiconductor and a data wire sequentiallyon the substrate; patterning the semiconductor and the data wire,wherein the data wire comprises a first data line, a second data line, asource electrode and a drain electrode, the second data line is spacedapart from the first data line, the drain electrode faces a part of thefirst data line and the second data line, and the source electrode isconnected to one of the first data line and the second data line;forming an organic insulating layer on the first data line and thesecond data line, the organic insulating layer having a contact holeexposing the drain electrode; and forming a pixel electrode on theorganic insulating layer, the pixel electrode electrically connected tothe drain electrode; wherein the pixel electrode comprises a first partoverlapping the first data line, and a second part overlapping thesecond data line, and wherein the width of the first part is differentfrom that of the second part.
 2. The method of claim 1, furthercomprising disposing an ohmic contact between the semiconductor and thedata line, and wherein the ohmic contact is patterned with thesemiconductor and the data wire.
 3. The method of claim 2, wherein thepixel electrode comprises a third part and a fourth part respectivelyoverlapping the gate line, and wherein the width of the fourth part isgreater than that of the third part.
 4. The method of claim 3, whereinthe fourth part has different widths.
 5. The method of claim 1, whereinthe pixel electrode is connected to the drain electrode through thecontact hole.
 6. The method of claim 5, further comprising forming astorage electrode making a storage conductor with the pixel electrode.7. The method of claim 6, further comprising forming a storage electrodeline on the substrate.
 8. A method for manufacturing a thin filmtransistor array panel comprising: forming a first gate line and asecond gate line formed on a substrate, wherein the first gate line isseparated from the second gate line, and comprises a gate electrode;disposing a semiconductor and a data wire sequentially on the substrate;patterning the semiconductor and the data wire, wherein the data wirecomprises a data line, a source electrode and a drain electrode, thedrain electrode faces a part of the data line, and the source electrodeis connected to the data line; forming an organic insulating layer onthe data line, the organic insulating layer having a contact holeexposing the drain electrode; and forming a pixel electrode on theorganic insulating layer, the pixel electrode electrically connected tothe drain electrode; wherein the pixel electrode comprises a first partoverlapping the first gate line, and a second part overlapping thesecond gate line, and wherein the width of the first part is differentfrom that of the second part.
 9. The method of claim 8, wherein thefirst overlapping area has different widths.
 10. The method of claim 9,further comprising disposing an ohmic contact between the semiconductorand the data line, and wherein the ohmic contact is patterned with thesemiconductor and the data wire.
 11. The method of claim 9, wherein thepixel electrode is connected to the drain electrode through the contacthole.
 12. The method of claim 11, further comprising forming a storageelectrode making a storage conductor with the pixel electrode.
 13. Themethod of claim 12, further comprising forming a storage electrode lineon the substrate.